C# - HttpWebResponse.StatusCode Not Trapping 500 Errors

Does a HttpWebResponse.StatusCode detect Asp.Net errors? Mainly a yellow screen of death? Some Background: I am working on a simple c# console app that will test servers and services to make sure they are still functioning properly. I assumed since the HttpStatusCodes are enumerated with OK, Moved, InteralServerError, etc... that I could simply do the following.

WebRequest request = WebRequest.Create(url);
request.Timeout = 10000;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
if (response == null || response.StatusCode != HttpStatusCode.OK)
{
// SERVER IS OK
return false;
}
else
{
// SERVER HAS SOME PROBLEMS
return true;
}

I found out this morning however that this doesn't work. An ASP.Net application crashed showing a Yellow Screen Of Death and my application didn't seem to mind because the response.StatusCode equaled HttpStatusCode.OK. What am I missing?

HttpWebResponse response;
try
{
response = (HttpWebResponse)request.GetResponse();
}
catch (WebException webexp)
{
response = (HttpWebResponse)webexp.Response;
}